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[Eckhart Aurelius Hughes]

Please use this topic to discuss "Many Worlds? An Introduction" by Simon Saunders which is the roughly 50-page-long introduction to the July book of the month, Many Worlds?: Everett, Quantum Theory, & Reality edited by Simon Saunders, Jonathan Barrett, Adrian Kent, and David Wallace. (The book is made up of 20 chapters, divided into 6 parts, plus the introduction at the beginning and a transcript at the end. We will discuss each chapter in its own topic, as well as a topic for the transcript and this topic for the introduction, giving us a total of 22 different topics for this book. I will create an organized linked list of all 22 discussions for ease of reference once we get into them.) You can read the introduction as well as some other parts on Google Books for free using their preview feature. I assume the free sample available through Amazon for their Kindle edition of the book also includes at least the introduction, and you do not actually need a Kindle to read the Kindle edition or the free sample. So please do not post in this topic until you have read the introduction. Considering that the introduction provides a summary of the entire book, please also use this topic for discussions about the book as whole or for discussing broader points in a cross-chapter context (e.g. for discussions comparing parts of multiple chapters), so we can keep the rest of the chapter-by-chapter topics each focused specifically on the respective chapter. For similar reasons, the poll in this topic will be for rating the book as a whole.

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What do you think so far after reading the introduction? If you have read the rest of the book, how well do you think the introduction covered the book? Do you think Saunders painted a fair picture of the arguments for and against the many worlds interpretation (MWI) in the introduction or do you think he was biased?

I could tell he supported MWI but I still think he did a reasonably good job writing a summary from an objective standpoint especially in regards to tone. One way I noticed he did this well was that when he used rhetorical wording or points he would do it in the context of paraphrasing, citing or summarize specific points made in other essays and especially in other essays in the book, which meant he as author still kept that quasi-journalist objectivity.

Most of the raw math and some of the other parts went over my head. One complaint I had about our previous book of the month, The Grand Design by Hawking and Mlodinow was that I felt they made things too basic. So far this book seems to have the opposite problem, it jumps in too deep too quick and its hard to follow along as a layman. As an introduction to MWI or worse yet as an introduction to Quantum Mechanics, and a basic understanding of the later seems to be a prerequisite to understanding the former, this introduction is no good. But I suppose it is not meant to be an introduction to MWI but rather an introduction to -- or quick, rushed summary of -- this book. Hopefully, the rest of the book doesn't get even harder to follow along and more complex, but rather the authors of each chapter take a little more time to explain some of the ideas involved in their arguments to help us non-experts follow along. In any case, despite some of the complex issues quickly rushed over, I think overall the introduction provides a decent broader context in which to prepare looking at more specific in-depth articles and points.

Overall, I am happier than expected about how much of this book seems to be philosophy rather than science.

One thing I love about this book is that it has plenty of specific citations and references that are well-organized. Other books of the month like On Kindness had a lot of lost potential because they lacked citations and for that matter helpful background or supporting data that would most warrant sources and citations.

Moving on, I have a few notes I took while reading the introduction.

On page 16 of my copy of the book, Saunders addresses a point I found fascinating about symmetry. It reminds me of an old philosophical question about a dog walking in a symmetrical room with two bowls of food and which food he eats. It takes some somewhat unrealistic assumptions to believe such a symmetry particularly for the likes of a dog, but as a thought experiment it addresses some presumably real issues. Such a philosophical quandary likely may have existed long before MWI. But Saunders using not a dog but a coin-flip makes me realize how MWI compliments that would-be problem:

As Wallace points out, at the heart of his arguments for the equivalence rule (and Deutsch's original argument) is a certain symmetry -- the case of the equi-amplitude outcomes--that cannot possibly be respected in any one-world theory. A tossed coin in any one-world theory must land one way or the other. However perfect the symmetry of the coin, this symmetry cannot be respected (not even approximately) by the dynamics governing its motion on any occasion on which it is actually thrown. But it can in Everettian quantum mechanics.

Whether one world or many, I doubt a dog in a room or a coin-flip ever really represents an equi-amplitude because in those cases I suspect the seeming symmetry is an illusion, i.e. made up of what Saunders may call an epistemic probability as opposed to an objective one, and a true symmetry at that macroscopic level might lead to highly unexpected results like a coin landing straight-up or cracking into pieces rather than landing on either side. However, the point of the thought experiment and thus the point in the quote by Saunders regarding true symmetry remains.

Here is another idea touched on that has me looking at things in a new light:

And betting, in the fission picture, at least once the structure of branching and amplitudes are all known, is a matter of caring about what goes on in some worlds, not beliefs about what happens in those worlds. In Albert's words: But remember (and this is the absolutely crucial point) that deciding whether or not to bet on E, in the fission picture, has nothing whatsoever to do with guessing at whether or not E is going to occur. It is, for sure. And so is -E. And the business of deciding how to bet is just a matter of maximizing the payoffs on those particular branches that -- for whatever reason -- I happen to care most about.

This seems to me to pretty much be an argument over semantics, but it's a useful one and this is a powerful albeit semantic argument for Albert's way of looking at things in my opinion. I find parallels between this argument regarding betting as a representation of preferences in MWI wit the kind of issues that come up when we question personal identity even in an assumed one-world reality that make us wonder why we might care about our future self more than anyone else now or in the future and even why anything matters when we will all be dead at some point.

Anyway, I am sure these issues will each be covered more specifically in later chapters. I am very interested to read the rest of this book.

[Quotidian]

I got the Kindle preview of this book, as recommended, and had a read through it. I am familiar with the Everett theory, but I find it outrageous, for reasons I will shortly explain.

My background is not science or physics, but philosophy, comparative religion and history of ideas. Obviously I am at a disadvantage in discussions of modern particle physics, because I don't 'do the math'. Everything I can grasp about it, which is probably not much, comes from what I can understand via the medium of text. I have discussed this idea on another forum with a contributor who claimed to be a physicist. He insisted that 'the many worlds interpretation' didn't really mean that there were 'many worlds'. I protested that this is what Everett did seem to say, but he simply pulled rank on me. 'I'm a physicist, and you don't understand the math'.

He had me there.

Apart from school science, which I was terrible at, I have read several books by science author Paul Davies, which I like and recommend. I subscribe to New Scientist magazine - ditto. I find Davies an excellent popular science writer, because he is very insightful from a philosophical perspective, but also works hard at being an impartial commentator on the difficult conundrums that modern physics has thrown up, as well as being an acknowledged expert in physics and cosmology. I have also attempted to read Brian Greene's 'Fabric of the Cosmos', although I will admit, that mostly amounts to reading particular passages which bear on certain philosophical issues.

So, all that said, what do I make of Everett's 'Many Worlds'. Well, my instinctive, gut-level reaction is that the idea is completely preposterous. I am somewhat heartened by the fact that I am not the only person who thinks this. But let's just look briefly on the central idea, summarized as follows in the Standord Encyclopedia of Philosophy:

The fundamental idea of the MWI, going back to Everett 1957, is that there are myriads of worlds in the Universe in addition to the world we are aware of. In particular, every time a quantum experiment with different outcomes with non-zero probability is performed, all outcomes are obtained, each in a different world, even if we are aware only of the world with the outcome we have seen.

Now, there are many reasons I find this preposterous.To start with, the many other versions of 'me' that exist in these other universes also find it preposterous, but all for slightly different reasons. Then there are all the versions of me that finds it perfectly sound - also for an infinite variety of reasons. That strikes me as an obvious failure of Ockham's razor, apart from anything else.

But to go straight to the main point - the problem is that I can't help but regard this kind of thinking as a signifier of some kind of colossal failure or crises. In Karl Popper's terms, Many Worlds doesn't amount to a scientific hypoethesis, because it cannot be falsified. If there are indeed 'many worlds in this universe that we are not aware of', then Carl Sagan's 'Demon Haunted World' has more than just a foot in the door. Thar be Dragons. And there is no way that 'natural philosophy' is able to ascertain the reality or otherwise of 'other universes' - not unless it wants to venture into some territory that looks suspiciously 'beyond nature'. So I can't help but think this is simply a model, or an idea, that is thrust upon us by the consequences of quantum mechanics. It gets us out of some kind of epistemological bind that has been thrown up in the atom smashers, which our theories can't otherwise explain.

I am very suspicious of the use that is made of 'multiverses' and 'many world theories' in modern thought. I would like to know what would be the result of NOT having the infinite elbow room that MWI provides. Such ideas can be used to validate all kinds of outlandish (now there's an ironic term, in the circumstances) theories. "Oh, but in some universe it might be X'. This is routinely invoked in all kinds of arguments - you even see it on philosophy forums, as it has entered the popular imagination (along with black holes, teleportation and dark matter.)

One question I have is, how many scientific grants are being underwritten by this kind of thinking, right now? And what would happen if, suddenly, something was found which made it clear that there weren't multiple universes or worlds? Although it is obviously hard to imagine what that might be - it is hard to prove a negative, as is often said.

So, what I am getting at, if MWI is the solution, what is the problem? It must be a pretty serious problem, to go to these lengths. What is the conclusion that we would be forced to accept, if MWI was decided not to be true?

I guess I will have to read some more of the book.

[Stanley Huang]

Quotidian said: “My background is not science or physics, but philosophy, comparative religion and history of ideas. Obviously I am at a disadvantage in discussions of modern particle physics, because I don't 'do the math'. Everything I can grasp about it, which is probably not much, comes from what I can understand via the medium of text. I have discussed this idea on another forum with a contributor who claimed to be a physicist. He insisted that 'the many worlds interpretation' didn't really mean that there were 'many worlds'. I protested that this is what Everett did seem to say, but he simply pulled rank on me. 'I'm a physicist, and you don't understand the math'.”

Well, at least you honestly describe what you feel and you do not need to be Einstein to talk or ask questions.

But if you read the Mahayana sutras, it also talks about many universes. You said that you are interested in religion. In the Mahayana sutra, it talks about how there are many Buddhas creating many universes.

So this is why I feel many universes may not be a new idea invented by modern physicists, because the Mahayana sutras had already talked about it before Einstein.

Einstein talked about the relativity of time. But what Einstein said may not be totally new, because in the Mahayana sutra, it also talks about the relativity of time.

It talks about how the god in heaven may experience a faster flow of time relative to the people on earth.

Modern physicists are interested in Zen, interested in Eastern thinkers.

The bible did not talk about many universes or the relativity of time.

So this is why I feel the books in the East are more than the bible.

Modern string theorists say that it is possible that there are many universes, but because of our technology is unable to detect a particle that small, there is no experiment to show.

So this is why a professor said: “Science is based on what you can see. Is string theory a philosophy or a theory or science? You tell me.”

But even if there is no technology to detect a particle that small, it may not mean that there is no possibility for many universes.

Because if there is no experiment to show that string theory is right, but there is also no experiment to show that string theory is wrong.

To me, I feel it is possible that there are infinite numbers of universes.

But experiment?

Before, I have read a book where author asks question: Is science possible?

What he is saying is that scientists seem to go beyond what modern technology can detect and is it possible or is science abstract?

And also there are people searching for theory of everything, which people ask: “Is it possible to have a theory that is perfect?”

I will end myself with a quote from Socrates, where he said: “One thing I know is that I know nothing.”

Thank you.

[Quotidian]

But if you read the Mahayana sutras, it also talks about many universes.

They talk about many worlds, and there's a difference, although it is true that some of them have a cosmic outlook, which is a remarkable fact in itself.

The point, for me, is that science is supposed to be an arbiter of what is possible. When science starts to talk about infinite branching universes in which all possibilities are actualized, I am inclined to think there is a big problem.

As I said, if Many Worlds is the solution - what is the problem?

Must be a big problem.

[Stanley Huang]

Why many worlds are a problem? I do not understand. What is wrong if there are many worlds? Wouldn't it be exciting if there are many universes?

[Eckhart Aurelius Hughes]

So, what I am getting at, if MWI is the solution, what is the problem? It must be a pretty serious problem, to go to these lengths. What is the conclusion that we would be forced to accept, if MWI was decided not to be true?

The problem is explaining wave function collapse. Without MWI, it seems one has to accept the absence of causal determinism.

[Sy Borg]

It's hard to feel qualified to comment. I'm not inclined to disagree in physics with an author who writes:

If for k≠j|c_k|≠|c_j|, then the bases{φ_k} in H^A, and {ψ_k} in H^B are unique. Eq. (5) is the Schmidt decomposition. If these bases diagonalize Pα and Pβ respectively, then (for any dimensionality)

Physics questions remain open while those with advanced mathematical tools disagree with each other.

There does not, in general, exist anything like a single state for one subsystem of a composite system. Subsystems do not possess states that are independent of the states of the remainder of the system, so that the subsystem states are generally correlated with one another. One can arbitrarily choose a state for one subsystem, and be led to the relative state for the remainder.

Thus we are faced with a fundamental relativity of states, which is implied by the formalism of composite systems. It is meaningless to ask the absolute state of a subsystem — one can only ask the state relative to a given state of the remainder of the subsystem, (Everett [1957 p.143]

The relativity issue inherently casts doubt on the completeness of our observations. All phenomena are necessarily be affected by the dynamics of their encompassing and granular systems. So this problem doesn't only pertain to "subsystems" because everything is a subsystem of a larger one. We can't don't know how much more there is to find at the scales of the very large and very small.

My gut feeling is that, just because different probabilities may occur it doesn't mean that they necessarily do. In a sense, probabilities compete for realisation in the informational domain in a similar way to nature's physical competition for survival.

[Airkarservices]

Nice post